The present invention relates to a multimedia system which distributes information from a central location, such as a central station or central office, to one or more subscribers, and in particular, to a switchable system which selectively distributes information to each of the subscribers from the central location.
With increasing bandwidths available on fiber optic communication paths, information providers are now capable of delivering a broader range of information, i.e., high definition video, to a subscriber premises. However, even with advancements in optical fiber telecommunication technology, theft of services remains a growing concern among information providers (e.g., cable television). The problem involves the fact that once a central station distributes signals in a general manner to a subscriber premises, the central station loses control of the signals. As a result, such signals are exposed to theft which results in a loss of revenue.
Presently, one approach to remedy the theft problem is to transmit scrambled signals or channels to each subscriber""s premises. Each subscriber premises is equipped with a smart set top box to descramble those signals or channels ordered by the subscriber. Such systems however require additional equipment, specifically scramblers and descramblers, which increases their overall cost. Moreover, intelligent set top boxes that permit theft of services are presently available on the black market. Such set tops are capable of descrambling all scrambled signals transmitted to the subscriber premises, thereby allowing the subscriber access to those signals or channels.
Another approach to remedy the problem is found in U.S. Pat. No. 4,994,909 (Graves et al., hereinafter Graves). Graves provides a video signal distribution system that includes a services switching device and an optical network interface (ONI) for selecting particular signals for delivery to a subscriber. The services switching device employs multiplexers for producing time-division multiplexed (TDM) signals. Because the processing and routing of TDM signals is typically accomplished utilizing electronics, a drawback of the Graves system is a need for optical-to-electrical and electrical-to-optical conversion and for controlled environmental vaults, power back-up and maintenance.
A better multi/demultiplexing technique that employs optical rather than electrical multiplexing involves the utilization of wavelength division multiplexing (WDM). WDM provides significant advantages over TDM. Specifically, wavelength multiplexed channels can be separated and combined passively, independently of the format and bit rate of the data being transferred. An example of a fiber optic subscriber loop architecture utilizing WDMs is found in U.S. Pat. No. 5,221,983 (Wagner). However, such subscriber-type systems employing WDMs neither provide or suggest any mechanism for selecting particular signals for delivery to a subscriber premises.
Accordingly, it is an object of the present invention to provide a fiber optic subscriber loop architecture, based on WDM techniques, which is capable of selectively transmitting only those bands ordered by the subscriber to the subscriber premises.
It is a further object of the invention to eliminate the need for scramblers and descramblers at the subscriber premises and, thus, reduce the overall cost of the system.
Another object of the invention is to prevent theft of information services.
Besides the aforementioned shortcomings and limitations of the prior art, the subject matter of the present invention also addresses methodologies and concomitant circuitry for overcoming the limitations and deficiencies relating to wideband transmission to the subscriber premises, especially wideband digital services. In providing these services, the information destined for the subscribers is digitally encoded, typically using the MPEG or MPEG-2 (Moving Pictures Expert Group) standard, and propagated as a digital stream over the transmission medium; digital encoding is deployed to effectively utilize the bandwidth of the medium. Because of the front-end encoding, the receiver at each customer premises requires a digital decoder to reconstruct the original information. Moreover, if two-way or bi-directional communication is desired, then the equipment at the customer premises must be arranged with a digital encoder. The decoding/encoding required by the customer""s equipment is expensive. Moreover, it is virtually impossible with such an arrangement to deliver tailored services, that is, subscriber-dependent services, to each individual subscriber.
To overcome the limitations of encoded digital propagation, some recently devised systems focus on non-encoded propagation so that the subscriber""s TV may be used in the conventional manner to receive the transmitted signals. Representative of such technology using a single-fiber for a transmission medium is a system for propagating a plurality of downstream video channels over the single fiber in combination with two-way interactive telephony communications over the same fiber, as disclosed in the article entitled xe2x80x9cLaunch of xe2x80x98CATV Video Distribution Servicexe2x80x99 over FTTHxe2x80x9d, authored by H. Ogura et al and published in the NTT Review, Vol. 9, No. 6, November 1997. As described in this article, two or more communications channels are delivered over a single optical fiber from a head-end to a subscriber""s home to effect fiber-to-the-home (FTTH) service. In general, the design philosophy for this system is one of separating downstream video from interactive, non-video communications, that is, propagating the downstream video at one wavelength (namely, 1.5 micrometers) and the interactive telephony communications at a second wavelength (namely, 1.3 micrometers). Moreover, th.is bidirectional telephony arrangement uses TCM (time compression multiplexing) in the so-called xe2x80x9cping-pongxe2x80x9d communication mode, wherein all downstream receivers detect the same signal, and each upstream communication from a given subscriber is assigned a unique time slot.
In particular, each subscriber is directly connected to the head-end with a dedicated fiber so every customer receives the same downstream signal broadcast from the head-end, that is, there is no ability to deliver to a given subscriber selected ones of the video channels composing the propagated downstream signal; such an arrangement is typically referred to as a xe2x80x9ctree-and-branchxe2x80x9d delivery system. Consequently, there is the potential for fraudulent use of the services as alluded to above. In addition, to derive the signal for the subscribers, a number of signal splitters are deployed. This means that the signal delivered to front-end of the cascade of splitters must have a high power level; high power components tend to be more costly.
Moreover, the system was designed to be implemented on already existing 1.3 micrometer zero-dispersion fibers to reduce implementation costs, but the downstream video utilizes the 1.5 micrometer wavelength for propagation. When a 1.5 micrometer optical wavelength is transmitted through a 1.3 micrometer zero-dispersion fiber, fiber dispersion induces a degradation with a concomitant deterioration in video quality. Consequently, the system must be arranged with dispersion compensation, which adds to the complexity and cost.
Also, the types of interactive services taught or suggested by this reference are existing services such as POTS and narrowband ISDN. There is no teaching or suggestion of using the interactive services part of the system (1.3 micrometer wavelength) for video, especially video conferencing, or wideband data. In brief, the system of Ogura et al separates video (downstream at 1.5 micrometers) from telephony (upstream and downstream at 1.3 micrometers) using a tree-and-branch delivery system for downstream transmission. This is in contrast to the present inventive subject matter, wherein the wavelength assignments are characterized as separating downstream from upstream, irrespective of the content of the downstream or upstream signals, and the system is arranged as a xe2x80x9cstar-deliveryxe2x80x9d system.
Thus, another object of this invention is to implement an embodiment which switches electrical signals as an alternative to an embodiment which switches optical signals.
It is still another object of the invention to house components sensitive to the environment in well-controlled environments such as a central office or a customer""s premises.
Yet another object is that of configuring a xe2x80x9cstar-deliveryxe2x80x9d system between the central location and each customer premises.
These shortcomings as well as other limitations and deficiencies are obviated, in accordance with the present invention, by a system which utilizes a dedicated fiber optic cable interconnecting a customer""s premises to a central location to propagate a downstream optical signal derived from a plurality of signals, either electrical or optical depending upon the embodiment, that are switched at the central location, the signals selected being only those signals subscribed to by the customer.
Briefly, in accordance with one broad system aspect of the present invention, the system for communicating between each particular customer and the central location over the dedicated fiber includes: (a) an electrical switch, at a central location, for selecting only those signals subscribed to by each subscriber, the electrical switch operating in response to control signals available at the central location; (b) an electrical-to-optical converter to generate an optical downstream signal from the selected electrical signals for propagation over the single fiber; and (c) an optical-to-electrical converter for converting the downstream optical signal delivered by the single fiber to received versions of the original electrical signals.
Moreover, bi-directional communications is effected by further arranging the system for transmitting second electrical signals between the central location and the customer""s premises, the electrical-to-optical converter being adapted for receiving the second electrical signals at its input and for changing the downstream optical signal in correspondence to the second electrical signals, and the optical-to-electrical converter being adapted for converting the detected downstream optical signal into second electrical received versions of the second electrical signals for use by the customer. For upstream communication to complete the bi-directional operational mode, the system is arranged with an upstream electrical-optical converter, at the customer""s premises, for converting third electrical signals into an upstream optical signal, and for transmitting the upstream optical signal over the optical fiber at a second optical wavelength, and wherein the central location further includes an upstream optical-electrical converter for detecting the upstream optical signal and for converting the upstream optical signal to detected electrical versions of the third electrical signals. Typically the third electrical signals are the counterparts to the second electrical signals which, when paired, effect the bi-directional communication mode.
The present invention provides an improved fiber optic subscriber loop architecture which reduces the overall cost of the system and prevents theft of services. Such a system selectively transmits only information ordered by the subscriber to the subscriber premises and, thus, eliminates the need for scramblers (at the central office or network node) and descramblers (at the subscriber premises). This results in a reduction in equipment and cost of the overall system. Such an arrangement also prevents unauthorized use or access (i.e., theft) of information services by a subscriber premises.
Other and further objects, advantages and features of the present invention will be understood by reference to the following specification in conjunction with the annexed drawings, wherein like parts have been given like numbers.